Non-Destructive Testing – NDT
Ultrasonic testing(UT) is carried out using sound waves. Sound moves in a straight line in metal. At a transition between two materials sound waves are reflected. This phenomenon is used to detect irregularities. All materials that can be penetrated by ultrasonic waves are suitable for this method: metal, aluminium, copper, stainless steel etc.
Ultrasonic testing enables faults deep in the material to be detected in different materials over their whole thickness, without having to carry out destructive tests. Ultrasonic testing is also faster than radiography.
Applications: wall thickness measurements, crack detection, weld examination, detection of corrosion/erosion.
Magnetic testing(MT) makes it possible to identify faults on and directly below the surface. This can only be done in magnetisable grades of steel. Material is tested using a magnetic field and test ink. Cracks, binding faults etc. interfere with the magnetic field.
Applications: surface-examination of welds, high-pressure steam piping, welding of supports, lifting lugs, stay rope attachments etc.
Penetrant testing (PT) is a surface-examination that can be carried out on all non-porous materials. A liquid – a ‘penetrant’ – is applied to the material surface. This penetrant then penetrates through into the damage. Another substance – the developer – shows where the penetrant has been absorbed into the damage.
Applications: all non-porous materials, surface testing of welds new build or maintenance, welding of supports, lifting lugs, stay rope attachments etc.
Radiographic Testing(RT) is the most commonly known non-destructive test method. Radiography can be used to obtain permanent image of surface and sub-surface (embedded) discontinuities.
The same discontinuities can be radiographed again after a period of service life and the radiographs can be compared to measure the change in the size and shape of the discontinuity.
There are numerous applications of radiography in engineering applications. Some of the common uses are detection of surface and subsurface features of interest in welded parts, castings, forgings, wall thickness measurement, corrosion mapping, detection of blockages inside sealed equipment, detection of reinforcing material in concrete slabs, measuring bulk density of materials, measuring porosity in concrete, etc.